1. Field of the Invention
The present invention relates to a display device, and more particularly, to an apparatus and method for compensating images in a display device to reduce blocking artifacts that appear in the images.
2. Discussion of the Related Art
A variety of compression techniques have been used to increase image transfer rates and storage efficiencies. Recent transform techniques widely used for image compression include Discrete Cosine Transform (DCT) and wavelet transform. The DCT technique has been used for JPEG, MPEG, and H.26X, and the wavelet transform technique has been used for JPEG2000.
In block-based image coding techniques such as JPEG and MPEG, an image is divided into blocks of a specific size and each block is individually encoded, and the image is then compressed via a quantization process and variable length coding. Image compression is performed in the quantization process in which information loss occurs. Thus, an image obtained through inverse quantization differs from the original image. At more than a certain compression rate, the block-based image coding causes blocking artifacts in the decoded image due to discontinuous luminance of blocks of the image at the boundaries between the blocks. Images compressed at a high compression rate have serious blocking artifacts, and smooth areas in the images look as if they are composed of blocks of a specific size. Blocking artifacts reduce the image quality more significantly than a loss of details in the image caused by the compression. A number of methods have been suggested to remove such blocking artifacts.
A variety of studies have been conducted to reduce blocking artifacts in the block-based transform coding. Methods for reducing blocking artifacts can be mainly divided into preprocessing and post-processing methods. The preprocessing method essentially removes blocking artifacts by removing the causes of blocking artifacts in the encoding process, and the post-processing method removes blocking artifacts from decoded images. The preprocessing method cannot be applied to coding formats such as JPEG and MPEG whose encoding and decoding procedures have been standardized. Post-processing methods can be mainly divided into filtering methods and transform coding methods. The filtering method applies low pass filtering to the block boundaries on the assumption that discontinuous portions along the block boundaries have high frequency components. Although it can reduce blocking artifacts in real time, the filtering method has a problem in that it damages edge information of the original image. In the transform coding method, transform coding is performed on an image, signal processing is performed on transform coding coefficients to remove blocking artifacts, and inverse transform coding is performed to reconstruct the image. However, it is difficult for the transform coding method to reduce blocking artifacts in real time since it requires a great deal of calculation.